In conventional high electron mobility transistors (HEMTs), also referred to as heterostructure FETs (HFETs) or modulation-doped FETs (MODFETs), a current flows between source and drain terminals of the device even if the gate electrode is grounded. That is, a thin electrically conductive channel (inversion layer) exists between the source and drain terminals. As such, the device is commonly referred to as being normally-on.
The normally-on feature of HEMTs is an intrinsic property of e.g. GaN technology, and restricts the range of applications for GaN technology to those applications where a power supply is available to generate the negative voltages necessary to turn the GaN device off. Moreover, the normally-on feature complicates the design of the circuitry needed to drive GaN transistors. In particular, unintended short-circuits may occur due to the normally-on property of such transistors. The same problem arises with semiconductor components based on other semiconductor materials than GaN.
Hence, there is a need for an improved solution.